1. Field of the Invention
The present invention relates to a fluorine gas generator and, more particularly, to a fluorine gas generator for producing high-purity fluorine gas having a very low impurity content and suited for use in the process of manufacturing semiconductors and so on.
2. Description of the Prior Art
Fluorine gas is a basic gas indispensable in the field of semiconductor production, for instance. While it is used as such in some instances, the demand in particular for nitrogen trifluoride gas (hereinafter referred to as “NF3 gas”) and the like synthesized based on fluorine gas for use as cleaning gases or dry etching gases for semiconductors has been rapidly increasing. Further, neon fluoride gas (NeF gas), argon fluoride gas (ArF gas), krypton fluoride gas (KrF gas) and the like are excimer laser oscillator gases used in the step of patterning integrated semiconductor circuits, and the raw materials therefor in frequent use are mixed gases composed of a rare gas and fluorine gas.
Fluorine gas and NF3 gas to be used in the production of semiconductors and so forth are required to have a high level of purity with a minimum impurity content. On each actual site of production of semiconductors or the like, a required amount of fluorine gas is taken out for use from a fluorine gas-containing cylinder. Therefore, it is very important to secure and manage the sites of storage of gas cylinders and the safety and purity of the gas. Furthermore, NF3 gas is rather in short supply due to the rapidly increasing demand therefor and, accordingly, a problem arises that a certain amount of the gas should be always in storage. When these factors are taken into consideration, installation of an on-demand and on-site fluorine gas generator at the place of use thereof is preferred to handling high-pressure fluorine gas.
Generally, fluorine gas is generated from such an electrolyzer as shown in FIG. 4. The electrolyzer body 201 is generally made of Ni, Monel, carbon steel, or the like. Furthermore, for preventing the hydrogen gas and fluorine gas generated from being mixed together, the electrolyzer body 201 is provided, at the bottom thereof, with a bottom plate 212 made of polytetrafluoroethylene or the like. The electrolyzer body 201 is filled with a mixed molten salt comprising a potassium fluoride-hydrogen fluoride system (hereinafter referred to as “KF—HF system”) as an electrolytic bath 202. The electrolyzer body is divided into an anode chamber or section 210 and a cathode chamber or section 211 by means of a skirt-shaped partition wall 209 made of Monel or the like. Fluorine gas is generated when electrolysis is conducted by applying a voltage between a carbon or nickel (hereinafter, “Ni”) anode 203 disposed within the anode chamber 210 and a Ni cathode 204 disposed within the cathode chamber 211. The fluorine gas generated is discharged through a discharge port 208, and the hydrogen gas generated on the cathode side is discharged through a hydrogen gas discharge port 207. The fluorine gas and hydrogen gas generated each contains a small amount of hydrogen fluoride gas (hereinafter, “HF”) coming from the mass retained in the anode chamber 210 and cathode chamber 211 and, for eliminating the same, each gas is passed through an HF adsorption tube connected to the downstream of each discharge port. When the level of the electrolytic bath lowers to a certain level as a result of fluorine gas generation, HF is fed directly to the electrolytic bath through an HF feeding line 213 extending from outside the electrolyzer to within the electrolytic bath in the cathode chamber. The feeding of HF is carried out in association with a sensor system (not shown) monitoring the level of the electrolytic bath. (Patent Document 1: Laid-open Japanese Patent Application (JP Kohyo) H09-505853).
However, since all relevant production plants are not always equipped with safety means exclusively for on-demand and on-site fluorine gas generators and since various gases are used or generated in or from fluorine gas generators, it is difficult to safely treat those gases which have incidentally leaked out of the fluorine gas generators due to some or other trouble. In every site of production, it is required that maintenance, exchange and other operations be easy to carry out. It has been found that there is a problem, namely such requirements cannot always be met.
The present invention, which has been made in view of the problems discussed above, has for its object to provide a fluorine gas generator with which the gases used or generated can be prevented from mixing together as far as possible in case of gas leakage and can be treated safely without allowing them to escape to the outside and with which maintenance, exchange and other operations can be carried out with ease.